An unambiguous approach is proposed for the measurement of the involvement of specific histones in the control of endogenous DNA polymerase activity in isolated rat hepatic nuclei and chromatin fractions. The approach results from the discovery by the applicant and colleagues that heparin, a histone-complexing agent, activates endogenous DNA polymerase in about 90% of chromatin, but not in a high specific activity chromatin fraction comprising only about 5-10% of total chromatin. Experiments are designed to: 1) Measure which histone(s) are removed by heparin from those chromatin fractions which contain DNA polymerase which is activated by heparin; 2) compare the histone composition of chromatin fractions which are activated by heparin with the histone pattern of the high specific activity fraction; 3) compare the histone patterns of the high specific activity fractions from normal and regenerating livers.